Metalation, especially lithiation, of halogenated polyolefins has long been recognized to yield useful intermediates. These intermediates can be used to produce graft copolymers, functionalized halogenated polyolefins and cross-linked copolymers.
One recognized process for achieving the subject metalation comprises reacting a low molecular weight lithium organic compound and a halide derivative of polyethylene or polypropylene. This reaction can be represented by the following: ##STR1## wherein R is a low molecular weight hydrocarbon radical, such as butyl, and X is a halogen, such as Cl. The lithium organic compound is provided in a molar amount about four times the molar content of the halogen in the polyolefin derivative. Th polyolefin derivative is added to the lithium organic compound which is at -20.degree. C. After addition, the temperature of the reaction mix is raised to 50.degree. C. to complete the desired reaction. The lithium organic compound is provided in a solvent such as heptane while the polyolefin derivative is solvated in anhydrous tetrahydrofuran for participation in the reaction. It is reported that there are two competing reactions, i.e., the Wurtz reaction and dehydrohalogenation. It is also possible that a third competing reaction, that is, alkylation of the polyolefin derivative, may also occur. These competing reactions are so significant that it is estimated that only about 22% of the halide reacted is replaced by lithium. The use of the large excess of lithium organic compound is reported to be necessary to achieve even this level of metalation. See: "Chemical Conversions of Halogenated Polyolefines Caused by Organo-Lithium Compounds", N. A. Plate et al, Vysokomol. soyed. 8: No. 9, pp. 1562-1567 (1966); "The Role of Chemico-Structural Effects in the Modification of Polymers", N. A. Plate, Vysokomol. soyed. A10: No. 12, pp. 2650-2661 (1968); and "Chemical Transformations and Catalytic Activity of Macromolecular Polylithium Compounds Polymerization", N. A. Plate et al, J. Polymer Sci.: Part C, No. 22, pp. 547-568 (1969).
Due to the competing Wurtz and dehydrohalogenation reactions, the resultant lithiated polymer product is not, strictly speaking, the HC-Li product shown by the above reaction but is rather a lithiated polymer which is cross linked, due to the Wurtz reaction, and has numerous unsaturated sites, due to the dehydrohalogenation reaction. Since an excess of lithium organic compound is used, the percentage of halogen sites involved in cross-linking, dehydrohalogenation and lithiation will be high, i.e., 40% to 70%. The high degree of cross-linking in the lithiated polymer product should evidence itself in the desired final product, be it a graft copolymer or a functionalized halogenated polyolefin, by rendering the final product more brittle and hard. Further, the loss of so many halide sites to dehydrohalogenation and lithiation will change the physical properties of the lithiated polymer product so that it will be more like a polyolefin than a halogenated polyolefin. For example, the elasticity exhibited by a chlorinated polyethylene starting material will be reduced in the more polyethylene-like lithiated polymer product. The greater the number of halogen sites used, the more polyolefin-like will be the lithiated polymer product.
Since a purpose of metalating a halogenated polyolefin is to ultimately yield a graft copolymer or a functionalized polymer having those properties which would be expected to be contributed by the starting halogenated polyolefin, the obtainment of a metalated more polyolefin-like product, due to the required use of an excess of metalating compound, is a definite drawback of this prior art process. Furthermore, the use of an excess of metalating compound also insures the presence, at reaction end, of unreacted metalating compound which, because of its high reactivity, can interfere with subsequent grafting or functionalization procedures. Still another drawback is that the metalating compounds are expensive and thus the required use of an excess of these compounds in the process makes the process less desirable from an economic standpoint.
Therefore, it is an object of the below described invention to provide a process for the metalation of halogenated polyolefins which process uses a metalating compound in a molar amount which is less than the molar amount of the halogen in the halogenated polyolefin and which, as a result, is capable of producing a metalated halogenated polyolefin which has had a low percentage of its halogen sites involved in cross-linking, dehydrohalogenation and metalation.